Health Questions and Answers

PREOPERATIVE RISK ASSESSMENT

What are the four essential “dos” of preoperative risk assessment?

  • Do interview and examine the patient with respect to major organ-system disease, and describe the extent, severity, and stability of each disease in your assessment.
  • Do explain to the patient your estimate of his or her risk of complications of anesthesia and surgery, and document the explanation in your consultation note.
  • Do specify how the patient’s current medications should be handled in the perioperative period.
  • Do make recommendations for venous thromboembolism prophylaxis in patients who may benefit.

List the three essential “don’ts” of preoperative risk assessment.

  • Don’t tell the anesthesiologist which type of anesthesia and anesthetic agent to use; this determination is the anesthesiologist’s job. The anesthesiologist relies on you for adequate characterization of the patient’s burden of medical disease.
  • Don’t “clear” the patient for surgery-such a step implies complete freedom from risk of adverse events, and we can never guarantee that a patient will not suffer an adverse outcome.
  • Don’t directly try to change a patient’s mind about proceeding with surgery-you are interfering in a patient-doctor relationship! Encourage patients to ask the surgeon questions about the proposed procedure. If you have serious concerns about surgery for a particular patient, call the referring surgeon and speak with him or her in a confidential manner and setting.

Describe general anesthesia (GA).
GA provides a loss of sensation with the loss of consciousness. Patients under GA may receive inhaled agents, inhaled plus IV drugs, or IV drugs alone. Ventilation may be managed through a mask, with or without an oropharyngeal or laryngopharyngeal airway, or through an endotracheal tube.
KEY POINTS: PURPOSE OF THE PREOPERATIVE RISK ASSESSMENT
1. Describe the patient’s current chronic diseases, their management, the patient’s level of symptomatology, and whether the diseases are stable.
2. Make an estimate of the patient’s risk of postoperative cardiac and noncardiac complications.

How is regional anesthesia (RA) different from GA?
RA uses local anesthesia to produce loss of sensation to part of the body. Examples include epidural, spinal, axillary, and other regional blocks. Patients receiving RA also may receive some sedation. A patient undergoing RA may need to receive GA if the block is not adequate.

Explain monitored anesthesia care (MAC).
MAC involves an anesthesiologist’s management of the patient during a procedure and may include provision of IV sedation, antiemetics or narcotics, and other pharmacologic treatments. MAC sometimes resembles GA in the amount of sedation produced in the patient.

List the three phases of GA.
Induction, maintenance, and reversal.

Define induction, and list some of the potential problems.
Induction of anesthesia consists of administering medication to the conscious, perceiving patient to produce a state of unconsciousness and lack of perception. Although inhalational agents can be used to induce anesthesia, in current practice induction usually is accomplished by the IV route. Although it is advisable to intubate some patients before induction, endotracheal intubation usually is carried out immediately after induction. Potential problems include retching, vomiting, aspiration, cough, laryngospasm, hypotension, and cardiac dysrhythmias.

Which anesthetic technique is safer for patients-spinal/epidural or general?
This is a trick question. The few available well-designed studies that have compared RA with GA found no difference in cardiac outcomes. GA with inhalational agents directly suppresses myocardial contractility and reduces functional residual capacity in the lungs, with increased mismatch of ventilation and perfusion. Hence, inhalational GA may not be optimal for patients with severe cardiac or pulmonary insufficiency. Although spinal and epidural blocks do not have these effects, patients receiving RA can develop hypotension and bradycardia. In addition, the patient’s airway is not as easily protected with RA. The higher the level of the spinal/epidural block, the more prominent the hypotension. Spinal and epidural blocks can be administered somewhat more quickly than GA.

What hemodynamic changes occur with spinal anesthesia?
Spinal anesthesia (the injection of local anesthetic into the subarachnoid space) blocks transmission of impulses from the sympathetic nervous system as well as impulses mediating motor and sensory functions. The sympathetic nervous system controls the caliber of the blood vessels. At basal levels of sympathetic tone, the vessels are maintained at about half their maximal diameter. Sympathetic stimulation causes vasoconstriction, whereas sympathetic enervation, as in spinal anesthesia, causes vasodilatation. Vasodilatation causes a drop in systemic vascular resistance and consequent pooling of blood in the lower extremities. Arterial blood pressure usually decreases with administration of spinal anesthesia, and the drop is more severe in patients who are volume-depleted before the anesthetic is given. Patients with hypertension (controlled or not) also tend to have exaggerated hypotensive responses to spinal anesthesia.

List the major clinical predictors of perioperative adverse cardiovascular events after noncardiac surgery.

  1. Unstable coronary syndromes
  2. Decompensated congestive heart failure (CHF)
  3. Significant arrhythmias
  4. Severe valvular disease
  5. Acute or recent myocardial infarction (MI)

What are the intermediate clinical predictors of perioperative adverse cardiovascular events after noncardiac surgery?
Mild angina pectoris, prior MI, compensated/prior CHF, diabetes mellitus, and renal insufficiency.

List the minor clinical predictors of perioperative adverse cardiovascular events after noncardiac surgery.
Advanced age, abnormal electrocardiogram, rhythm other than sinus, low functional capacity, history of stroke, uncontrolled hypertension.

Which surgical procedures place the patient at low risk (< 1%) of cardiac complications?
Endoscopic procedures, superficial procedures, cataract surgery, breast surgery.

Which surgical procedures place the patient at intermediate risk (< 5%) of cardiac complications?
Carotid endarterectomy, head and neck surgery, intraperitoneal and intrathoracic surgery, orthopedic surgery, prostate surgery.

List surgical procedures that place the patient at high risk (> 5%) of cardiac complications.

  1. Emergent, major surgery, especially in elderly patients
  2. Major vascular surgery, including aortic surgery
  3. Peripheral vascular surgery
  4. Prolonged surgery, with expected large fluid shifts and/or blood loss

Summarize the relationship of patient functional status to postoperative complications.
Poor functional status increases a patient’s risk of both cardiac and noncardiac complications of surgery. Assessment of functional status is an essential part of the American College of Cardiology/American Heart Association (ACC/AHA) perioperative assessment guideline.

How is functional status assessed?
Cardiologists express functional status in terms of metabolic equivalent (MET) levels. One MET is equal to the oxygen consumption (3.5 mL/kg/min) of a 70-kg, 40-year-old man in a resting state. With this benchmark, functional capacity is excellent in patients who can perform at a level of > 7 METs; moderate at 4-7 METs; and poor if patients cannot meet a 4-MET demand during most daily activities. The 4-MET cut point is used in the ACC/AHA guideline.

Which specific activitites indicate that a patient’s functional status is acceptable?

  1. Brisk walks of at least several blocks
  2. Climb at least one flight of stairs
  3. Heavy housework such as scrubbing tiles and floors and moving furniture
  4. Golfing (without a cart) and participation in team sports such as doubles tennis or pitching in baseball
  5. More strenuous activities (which approach 10 METs or more in energy consumption), including swimming, singles tennis, basketball, and skiing.

Summarize the ACC/AHA approach to patients with major clinical predictors of cardiac risk.
Patients with major clinical predictors of cardiac risk (see question 11) should be evaluated and stabilized before elective surgery.

What are the ACC/AHA guidelines for patients with intermediate clinical predictors of cardiac risk?
Patients with intermediate clinical predictors of cardiac risk who have poor functional status (< 4 METs) or moderate or excellent (> 4 METs) functional status but who are undergoing high surgical risk procedures should undergo noninvasive cardiac testing to refine risk assessment. Patients with intermediate clinical predictors who are undergoing low surgical risk procedures and patients with moderate to excellent functional status who are undergoing procedures of no more than intermediate risk may go to the operating room without further cardiac evaluation.

Summarize the ACC/AHA guidelines for patients with low clinical predictors of cardiac risk.
Patients with minor or no clinical predictors should undergo noninvasive testing only if they have both poor functional status (< 4 METs) and are scheduled to undergo a high surgical risk procedure. All other patients with minor or no clinical predictors may go directly to the operating room.
KEY POINTS: INDICATIONS FOR PREOPERATIVE NONINVASIVE CARDIAC TESTING

  • Patients with intermediate clinical predictors who cannot exert to above 4 METs and need moderate- or high-risk surgery.
  • Patients with intermediate clinical predictors who can exercise to 7 METs but need high-risk elective surgery.
  • Patients with minor or no clinical predictors who cannot exercise to 4 mets and need high-risk elective surgery.
  • Patients who would be candidates for interventions were they not having surgery.

What is the prevalence of underlying coronary artery disease (CAD) among patients with peripheral vascular disease?
Patients with peripheral vascular disease are highly likely to have CAD. Among 1000 consecutive patients with vascular disease but no clinical evidence of CAD who underwent coronary angiography, 37% had at least one coronary artery stenosis > 70%. This can be considered the minimal pretest probability of CAD in a population of patients under consideration for peripheral vascular surgery. However, many patients with vascular disease may have some clinical evidence of CAD, and in such patients the prevalence is far higher. Thus, for the patient population as a group, the incidence is approximately 60%.

Discuss the major complication of the cross-clamping procedure and related maneuvers in repair of an abdominal aortic aneurysm.
Ischemia can result in the territories that are served by the clamped arteries. Decreased blood flow during the cross-clamping can result in a number of complications caused by ischemia, including acute renal failure, bowel infarction, and spinal cord damage that may result in paraplegia.

What is the risk of embolization of cholesterol fragments into the peripheral circulation?
Embolization of cholesterol and atheromatous fragments from the diseased aorta into the peripheral circulation is a rare complication. Although embolization can result from any angiographic procedure in which an atheromatous blood vessel is cannulated, a study obtained through a femoral artery seems to pose the highest risk.

What types of damage may result from embolization?
A shower of cholesterol emboli causes ischemic damage to the skin, extremities, and visceral organs (e.g., intestines and kidneys). Small emboli to the kidneys can cause progressive renal failure; large emboli can obstruct the main renal arteries and cause fulminant acute renal failure.

What factors are associated with a higher risk of cholesterol emboli syndrome?
Clues to the diagnosis of cholesterol emboli syndrome include a predisposing procedure in a patient with extensive vascular disease; the presence of leukocytosis, and especially eosinophilia, in the peripheral blood film; and cholesterol crystals in tissue specimens and retinal arteries.

Why do general anesthesia and surgery carry a higher risk for perioperative cardiac complications in patients with asymptomatic but significant aortic stenosis (AS)?
AS presents a fixed obstruction to the outflow of blood from the left ventricle (LV). In other words, the stenotic orifice limits maximal cardiac output (CO). In patients with moderately severe AS, arterial dilatation has little ability to increase the CO, because the stenotic valve remains the major obstruction to outflow. Because such patients do not have the normal response to peripheral dilatation, they are prone to hypotension with exercise or other situations in which peripheral dilatation is induced (e.g., anesthesia). Furthermore, because of LV hypertrophy such patients have stiff ventricles so that, for any given intracavitary volume, the pressure is higher than normal. When cardiac return is increased in an effort to augment CO, there is the potential for rapid rises in filling pressures with resultant pulmonary edema.

What specific complications may develop in patients with AS?
At the time of surgery, patients with AS are at risk for hypotension, pulmonary edema, and MI. Ischemia can develop in patients with AS for several reasons. First, atherosclerotic coronary disease frequently coexists with AS. In addition, the pathophysiologic features of AS also affect myocardial oxygen balance unfavorably. Myocardial hypertrophy is associated with an increase in myocardial oxygen demand, and decreases in aortic pressure, especially during diastole, lead to decreases in myocardial oxygen delivery.

What are the risk factors for perioperative MI with noncardiac surgery?
In theory, anything that increases myocardial oxygen demand or decreases oxygen supply to the myocardium so that irreversible cell injury occurs is a risk factor for perioperative MI. In practice, however, because of the remarkable range of the autoregulation of perfusion across the coronary bed in people with normal coronary arteries and myocardium, the most important risk factor is heart disease (e.g., stenotic coronary arteries, hypertrophied muscle, dilated chambers). These conditions make the heart less able to compensate for the perturbations of myocardial oxygen demand and supply that may occur with anesthesia and surgery. Sustained hypotension intraoperatively seems to be the most important extraneous risk factor. Sustained intraoperative hypertension does not seem to be as important.

Which surgical patients should undergo surveillance testing for perioperative MI?
Patients with known or suspected CAD who undergo high-risk procedures should be considered candidates for electrocardiograms performed at baseline, immediately after surgery, and on postoperative day 2. Biomarkers such as creatine kinase and troponin levels may also be performed in these patients or only in those with electrocardiographic or clinical evidence of cardiovascular dysfunction.

Summarize the principles of evaluation and management of patients with CHF who must undergo noncardiac surgery.
Whether CHF results from systolic impairment or diastolic dysfunction, determining the state of compensation is the most important component of the preoperative evaluation-even more important than the ejection fraction. The ejection fraction tells nothing about the state of compensation, and no consistent relationship has been found between ejection fraction and exercise tolerance as determined on a treadmill. It is important to have the patient as well compensated as possible before surgery. CHF is an independent risk factor for perioperative cardiac complications.

What are the symptoms and signs of decompensation?
New or recent declines in exercise tolerance, increasing fatigue, orthopnea, and paroxysmal nocturnal dyspnea are the symptoms of decompensation. The signs of decompensation are weight increase, jugular venous distention, S3 gallop, hepatomegaly, and edema.

Explain the significance of postoperative atrial fibrillation (AF).
AF is common after intrathoracic or cardiac procedures, which may directly irritate the atria and precipitate fibrillation. Patients with chronic pulmonary or cardiac disease also may develop atrial fibrillation because of the combination of the disease and the high catecholamine state that exists after surgery.

How are patients with postoperative AF treated?
The evaluation and management of patients with postoperative AF are similar to those for nonsurgical patients. One difference is that, wherever possible, beta blockers or calcium channel blockers are preferred over digoxin for ventricular rate control. These drugs counter the excessive postoperative catecholamines and have anti-ischemic effects, which also may be beneficial. AF often resolves relatively quickly, but if it persists, the patient should be anticoagulated, if possible, to prevent development of atrial thrombus and embolic stroke.

What are the clinically significant pulmonary complications of surgery?
Any pulmonary abnormality that affects the clinical course of the surgical patient is considered clinically significant. Examples include:

  • Atelectasis
  • Infection, including bronchitis and pneumonia
  • Prolonged mechanical ventilation and respiratory failure
  • Exacerbation of chronic obstructive pulmonary disease (COPD)
  • Bronchospasm

What are the definite risk factors for postoperative pulmonary complications?

  • Upper abdominal or thoracic surgery
  • Surgery lasting more than 3 hours
  • Poor general health status, as defined by high ASA class
  • COPD
  • Smoking history within the past 8 weeks
  • Use of pancuronium as a neuromuscular blocker

List the probable risk factors for postoperative pulmonary complications.
General anesthesia (versus spinal or epidural anesthesia), obesity, and PaCO2 > 45 mmHg.

List the possible risk factors for postoperative pulmonary complications.
Current upper respiratory tract infection, abnormal chest radiograph, and age.

Which surgical patients should undergo preoperative spirometry?
The only group for whom preoperative pulmonary function tests (PFTs) are mandatory is the group under consideration for lung resection. For all other types of surgery, there is no absolute minimal lung function, as assessed by PFTs, for avoidance of postoperative pulmonary complications. In other words, even patients with severe COPD can be managed perioperatively with a satisfactory outcome. Patients with unexplained pulmonary symptoms may benefit from preoperative PFTs, as well as those whose symptoms due to known COPD or asthma may not be optimally controlled.

Which surgical patients should undergo preoperative arterial blood gas (ABG) analysis?
Patients with a PaCO2 > 45 mmHg are at increased risk for postoperative complications. Such patients usually have underlying severe COPD. The ACP recommends preoperative ABG testing for patients undergoing coronary bypass surgery or upper abdominal surgery who have a history of smoking or dyspnea and for patients undergoing lung resection.

Which preoperative strategies help to reduce the risk of postoperative pulmonary complications in patients with chronic pulmonary disease?

  • Smoking cessation 8 or more weeks before surgery
  • Inhaled ipratropium for all patients with clinically significant COPD
  • Inhaled beta agonists for patients who wheeze or are dyspneic
  • Preoperative systemic corticosteroids for patients who are not optimized to baseline at the time of surgery
  • Antibiotics for definite pulmonary infection
  • Teaching lung expansion maneuvers to patients before the surgery

List intraoperative strategies that help to reduce the risk of postoperative pulmonary complications in patients with chronic pulmonary disease.

  • Limit the surgical procedure and anesthesia to less than 3-4 hours in duration
  • Surgery other than upper abdominal or thoracic, when possible
  • Laparoscopic rather than open abdominal surgery, when possible
  • RA for very high-risk patients
  • Epidural/spinal anesthesia rather than GA for high-risk patients
  • Avoid use of pancuronium in high-risk patients

Which postoperative strategies help to reduce the risk of postoperative pulmonary complications in patients with chronic pulmonary disease?

  • Lung expansion maneuvers (deep breathing or incentive spirometry) in high-risk patients
  • Epidural anesthesia rather than parenteral narcotics

Describe the principles of management for asthmatic patients who must undergo nonpulmonary surgery.
The two major principles of managing asthmatic patients are control of bronchospasm and control of secretions. Tracheal intubation can exacerbate bronchospasm and also is associated with increased sputum production. This problem is minimized by ensuring that bronchospasm is under optimal control before the patient goes to the operating room. Inhaled bronchodilators should be administered on a regular schedule, and if the patient is receiving theophylline, the serum level should be kept in the therapeutic range. Secretions can be managed by a pulmonary toilet program perioperatively. Such a program includes incentive spirometry in addition to inhaled bronchodilators. Steroid-dependent asthmatics, in whom adrenal function is often suppressed, should receive IV corticosteroids in the perioperative period to cover the stress of anesthesia and surgery.

Are patients with obstructive sleep apnea (OSA) at increased risk for postoperative complications?
When patients undergo surgery, such as uvulopalatopharyngoplasty, to correct OSA, the most common complications are airway-related, but the complication rate is still low. There are no data about outcomes of other noncardiac surgical procedures in patients with OSA. In evaluating a patient with known OSA who is treated with continuous positive airway pressure (CPAP), the consulting physician should determine whether the patient is compliant. Noncompliance with CPAP is quite common. The physician should assess the patient for signs and symptoms of right heart failure. Room-air ABG and electrolyte analyses reveal CO2 retention consistent with inadequately treated OSA.

How can the risk of general medical complications be assessed in patients with chronic liver disease?
Patients with chronic liver disease are at increased risk for medical complications of surgery and anesthesia. The medical consultant should identify the nature of the liver disease (acute or chronic hepatitis and whether cirrhosis is present) and describe its severity. Most studies examining surgical outcomes have evaluated patients with cirrhosis. The Child-Pugh classification of cirrhotic severity has been shown to predict morbidity and mortality. Patients with acute alcoholic or viral hepatitis, fulminant hepatic failure, or severe and uncorrectable hypoprothrombinemia are not candidates for elective surgery.

What measures should be undertaken to prepare patients with chronic liver disease for surgery?

  • Treatment of hypoprothrombinemia with vitamin K or fresh frozen plasma to achieve a prothrombin time within 3 seconds of normal
  • Platelet transfusion to maintain a count of at least 100,000/mL
  • Cessation of all alcohol intake
  • Treatment and control of ascites with diuretics to reduce the risk of wound dehiscence in the abdomen
  • Correction of electrolyte abnormalities, such as hypokalemia
  • Consideration of perioperative nutritional support for malnourished patients who must undergo major surgery (e.g., hepatic resection/transplant)

Why is cessation of alcohol intake particularly important for patients with alcoholic hepatitis?
For patients with alcoholic hepatitis, cessation of alcohol intake may improve liver function indices. Some experts recommend serum gamma glutamyl transferase (GGT) as a useful marker of hepatic inflammation due to alcohol. GGT levels should return to normal 3-5 weeks after cessation of alcohol intake.

What tests should be performed before cataract surgery?
Schein and colleagues randomized over 18,000 patients at nine medical centers to undergo or not to undergo a standard set of preoperative tests (EKG, serum electrolytes, renal function, complete blood count) in addition to the history and physical examination. They found no difference in complication rates between the two groups overall, nor did specific subgroups based on characteristics such as age or medical history benefit from preoperative tests. Based on these results, it appears reasonable to forego routine blood work and EKG for patients whose history and physical examinations reveal no need for such evaluation.

What is the most useful screening tool for asymptomatic patients who may be at risk for perioperative bleeding due to hereditary hemorrhagic or coagulation disorders?
Patient history is the most useful screening tool for disorders that may cause perioperative hemorrhage, such as von Willebrand’s disease or hemophilia. All patients should be questioned about a personal or family history of excessive bleeding after prior surgeries, procedures, or childbirth; history of transfusions; and medication use that may be associated with acquired coagulation defects.

What lab tests are used to assess hemostasis?
A prothrombin time, activated partial thromboplastin time, and platelet count should be performed in patients undergoing procedures that have a low risk of hemorrhage (lymph node biopsies, herniorrhaphy, dental extractions), if their history suggests a possible bleeding disorder. Patients undergoing most other procedures have a higher risk of possible hemorrhage, and these tests should be considered independently of the history and physical examination. Additional tests will probably be necessary if one of these parameters is abnormal.

How should you determine the cause of new-onset renal insufficiency in postoperative patients?
In postoperative patients, as in other populations, it is useful to classify new-onset renal insufficiency as prerenal, renal, or postrenal.

What causes prerenal azotemia?
Prerenal azotemia results from decreased renal perfusion. Its causes include intravascular volume depletion due to hemorrhage, GI losses (as with nasogastric suction or ileostomy), or third-spacing of fluids (as with peritonitis); decreased cardiac function due to pump failure, valvular abnormalities, dysrhythmias, or pericardial tamponade; excessive peripheral vasodilatation as seen in sepsis or with afterload-reducing agents; and obstruction of blood flow through renal arteries or veins.

What causes postrenal azotemia?
Obstruction to urine flow causes postrenal azotemia. In the work-up of postoperative renal insufficiency, obstruction at or below the bladder neck should be ruled out by the insertion of a catheter. For obstruction above the bladder to cause renal failure, it must be bilateral. Inadvertent ligation of the ureters during abdominopelvic surgery occasionally occurs. The presence of hydronephrosis/hydroureter can be ascertained by renal ultrasonography.

List the causes of renal azotemia.
Causes of postoperative renal azotemia include ischemia, as may occur with abdominal aortic aneurysm surgeries, and exposure to nephrotoxins, such as contrast agents and aminoglycosides.

Which class of acute renal failure (ARF) causes is most common in surgical patients?
Prerenal causes account for 90% of postoperative ARF.

What is the incidence of perioperative ARF?
Perioperative ARF occurs in 1.2% of all surgical patients.

What patient-and surgery-specific characteristics are associated with perioperative ARF?
Elderly patients and patients with jaundice, chronic renal failure, CHF, or diabetes are at increased risk. Cardiac and aortic surgical procedures are associated with higher rates of perioperative renal failure.

Explain the mechanism of perioperative ARF.
The mechanism of the renal failure is most commonly ischemic injury to the kidney, which can be caused by intraoperative hypotension and cardiopulmonary bypass and aortic cross-clamping procedures related to cardiac and aortic surgeries. Another important cause of ARF in patients undergoing aortic surgery is renal artery cholesterol embolism after clamping and unclamping of the atherosclerotic aorta during repair of aortic aneurysm. In the most severe cases, patients develop sudden, complete anuria during the release of the cross-clamp, as a manifestation of bilateral renal artery embolism. A careful skin and ophthalmologic exam may reveal cholesterol emboli, which provide essential evidence for the diagnosis.

Are dialysis patients who undergo surgery at increased risk for adverse outcomes?
Yes. Dialysis patients appear to have an increased likelihood of postoperative complications compared with surgical patients with normal renal function and to require longer hospital stays, pressor support, and intensive care.

What causes postoperative complications in dialysis patients?

  1. High incidence of underlying coronary artery disease and myocardial dysfunction
  2. Lack of physiologic maintenance of volume and electrolyte status, leading to perioperative volume overload or sodium or potassium disturbances
  3. Underlying bleeding diathesis, leading to perioperative hemorrhage
  4. Poor blood pressure control
  5. Retarded excretion/metabolism of some anesthetics and analgesics

When should dialysis be performed in relation to elective surgery?
Most nephrologists recommend that patients with end-stage renal disease (ESRD) undergo dialysis immediately before surgery to optimize volume status and electrolyte levels.

Many patients with ESRD have a bleeding tendency. Should bleeding time be assessed before surgery?
No. Experts do not recommend using the bleeding time to screen patients because (1) a normal bleeding time does not predict the safety of surgery, and (2) a prolonged bleeding time does not predict hemorrhage. This finding may be due in part to the effect of technical factors in test performance. However, nephrologists do recommend assessment of the bleeding time before renal biopsy.

What causes platelet dysfunction in uremia?
Platelet dysfunction in uremia is probably multifactorial; causative factors include uremic toxins (hence performance of dialysis immediately before surgery is advisable), anemia, excessive parathyroid hormone, and aspirin use. Some patients with chronic renal disease are hypercoagulable; therefore, one should not assume that all dialysis patients are safe from acute venous thromboembolism.

How does perioperative bleeding due to uremia typically present?
Uremic bleeding usually develops as hemorrhage in the skin or oozing at sites of trauma or surgery. Therefore, bleeding from an organ should be evaluated with the appropriate diagnostic tests to identify a cause, such as peptic ulcer disease.

Summarize the treatment options for perioperative bleeding due to uremia.

  1. Transfusion to increase the hematocrit to 25-30%
  2. Desmopressin (DDAVP) at a dose of 0.30 μg/kg either intravenously or intranasally (onset of action = 1 hour, duration = 4-24 hours)
  3. Cryoprecipitate, 10 units IV every 12-24 hours (duration of effect = 8-24 hours)
  4. Conjugated estrogens, 0.6 mg/kg/day IV for 5 days; Premarin, 2.5-5.0 mg/day orally, or 50-100 μg transdermal estradiol twice weekly (onset at 1 day after initiation, peak effect 5-7 days later, duration of effect up to 1 week or more after cessation of therapy)
  5. Dialysis

What is the first step in the diagnostic approach to patients with postoperative hyponatremia?
The first step in the approach to patients with postoperative hyponatremia (serum sodium of 127 mEq/L) is to assess volume status by performing a physical examination. Three possibilities exist, each with its own differential diagnosis: volume depletion, edema, and euvolemia.

What causes volume depletion?
The volume-depleted patient is salt- and water-depleted, with the salt deficit exceeding the water deficit. The deficits result from either renal losses (e.g., diuretic excess) or extrarenal losses (e.g., GI losses).

Discuss the possible causes of edema.
The edematous patient has an excess of total body water and salt, with the water excess greater than the salt excess. The excesses result from the kidneys’ retention of salt and water in conditions such as cardiac failure and cirrhosis, in which the kidneys perceive a decrease in the “effective arterial blood volume.” Salt and water excesses also are seen in nephrosis and advanced renal failure, although the inciting causes are different.

Explain hyponatremia in the euvolemic patient.
The hyponatremic patient who appears to be euvolemic is usually modestly volume-expanded and has an excess of total body water, although this excess is not detectable on examination. The most likely explanation for “euvolemic” hyponatremia is prolonged release of antidiuretic hormone (ADH) in the face of persistent water intake. Postoperative pain is one stimulus for ADH release.

Summarize the role of measuring urinary sodum concentration in patients with hyponatremia.
Measurement of urinary sodium concentration is a useful adjunct in distinguishing among the diagnostic possibilities in the three categories. Hyponatremia is quite common in postoperative patients. Usually it results from a combination of hypotonic fluid administration and release of ADH.

Should postoperative adrenal insufficiency be a major concern?
Adrenal insufficiency in the perioperative period is rare. Although it is an eminently treatable condition, clinicians often omit it from the differential diagnosis of intra-or postoperative deterioration. Surgery is a physiologically stressful situation that may unmask chronic adrenal insufficiency.

What are signs and symptoms of adrenal insufficiency?
The first sign may be persistent intraoperative hypotension. Postoperatively, the patient may be febrile (to 103°F) with nausea, vomiting, and severe abdominal pain-findings that often are misdiagnosed as an intra-abdominal catastrophe. Hypotension and shock can develop. Whenever the diagnosis is entertained, a serum cortisol level should be drawn, and corticosteroids should be administered without waiting for the result.

What is the incidence of postoperative delirium?
In a prospective cohort study, Marcantonio and colleagues identified postoperative delirium in 9% of patients undergoing general, orthopedic, or gynecologic surgery at a single institution.

What risk factors may lead to postoperative dementia?
Multivariate analysis revealed the following independent predictors of delirium:

  1. Age > 70 years
  2. Alcohol abuse
  3. Poor cognitive status, as measured by the Telephone Interview for Cognitive Status (a score of 30 correlates with a score of 24 on the Mini-Mental Status Exam)
  4. Poor physical functional status, as measured by a class IV assessment according to the Specific Activity Scale (patients are unable to walk 4 km/hr for one block, make their bed, or dress themselves without stopping to rest)
  5. Preoperative electrolyte abnormalities: serum sodium < 130 or > 150 mmol/L, serum potassium < 3.0 or > 6.0 mmol/L, or serum glucose < 60 or > 300 mg/dL
  6. Aortic aneurysm surgery
  7. Noncardiac thoracic surgery

How can these risk factors be used to score the patient’s risk for postoperative dementia?
Each item in question 76 is scored with 1 point with the exception of aortic aneurysm surgery, which is scored with 2 points. In the validation study set, no patients with scores of 0 developed delirium, whereas 11% of patients with scores of 1 or 2 and 50% of patients with scores > 3 developed postoperative delirium.

How can the risk of perioperative venous thromboembolism (VTE) be assessed?
The numerous risk factors for VTE may occur in combination in a single patient, in which case their effect is cumulative. The risk assessment for each surgical patient must be comprehensive, taking into account medical history, current illness, and planned surgical procedure. The VTE risk factors can be grouped as negligible risk, increased risk, and moderate-to-high risk to facilitate the choice of prophylactic treatment.

Which factors indicate negligible risk of VTE?
Age under 40 years and absence of chronic medical illness.

Which factors lead to an increased risk of VTE?

  • Age over 40 years
  • General surgery
  • Acute MI admission
  • General surgery
  • CHF
  • Hyperhomocysteinemia
  • Antithrombin III deficiency
  • Use of oral contraceptives
  • Obesity
  • Protein C deficiency
  • Protein S deficiency
  • Factor V Leiden
  • Acute cerebrovascular accident with lower extremity paralysis
  • Pneumonia admission
  • Pregnancy
  • Malignancy
  • Prior VTE

Which surgical procedures involve a moderate-to-high risk of VTE?

  1. Knee or hip replacement
  2. Hip fracture
  3. Pelvic/lower extremity trauma
  4. Spinal cord injury

In which patients is VTE prophylaxis recommended?
In general, patients with negligible risk who are not undergoing a moderate-to-high risk (question 81) surgical procedure do not need VTE prophylaxis. Patients at highest risk for VTE are those who are undergoing major orthopedic procedures or have suffered pelvic or lower extremity trauma. Such patients warrant aggressive VTE prophylaxis with low-molecular-weight heparin or warfarin compounds, as do patients with multiple risk factors. Patients who combine high-risk surgery with at least several other risk factors should be considered for combined-modality prophylaxis (i.e., intermittent pneumatic compression plus low-molecular-weight heparin).

What is the optimal duration of VTE prophylaxis for patients undergoing total hip or knee replacement? For patients who have had repair of a hip fracture?
This is an area of ongoing inquiry. Such patients continue to be at risk for postoperative VTE after discharge from the hospital. In 2001, the Sixth American College of Chest Physicians Consensus Conference recommended that patients who have had total knee or hip replacement should receive 7-10 days of postoperative warfarin or LMW heparin but noted that optimal prophylaxis may actually be longer in duration. Newly published data suggest a benefit to extending prophylaxis with LMW heparin in hip replacement patients to 35 days postoperatively. Warfarin is stopped with discharge. Unfortunately, no such data exist for patients who have undergone surgery for hip fracture. The best course is to treat such patients with VTE prophylaxis until they are fully ambulatory.

Two days after repair of a hip fracture, an elderly patient develops sudden dyspnea and tachypnea. He has been receiving LMW heparin for VTE prophylaxis. What diagnosis must be ruled out first?
Despite VTE prophylaxis, there is a good possibility that the patient has sustained a pulmonary embolism. In randomized, controlled trials of interventions to prevent VTE in patients with hip fracture, the groups that received prophylaxis (low-dose or LMW heparin or low-intensity warfarin) had a DVT prevalence of 24-27% by venogram (compared with 48% for the control/placebo groups). Thus, some patients who have received prophylaxis develop VTE, and the medical consultant and orthopedist must maintain a high index of suspicion.

What is malignant hyperthermia?
Malignant hyperthermia is a rare genetic disorder that develops in response to treatment with certain anesthetic agents, most commonly succinylcholine and halothane. The onset is within a few hours of anesthetic administration.

What clinical findings are associated with malignant hyperthermia?
Clinical findings include muscle rigidity, sinus tachycardia, cyanosis, and mottling of the skin, closely followed by marked hyperthermia with temperatures possibly as high as 45°C. Hypotension, arrhythmias, rhabdomyolysis, electrolyte disorders, and disseminated intravascular coagulation may ensue rapidly. The full syndrome can develop without hyperthermia, although this occurrence is rare.

How is malignant hyperthermia treated?
Dantrolene is the treatment of choice and should be administered as quickly as possible to ensure survival. Dantrolene is a nonspecific skeletal muscle relaxant that acts by blocking release of calcium from the sarcoplasmic reticulum. It should be given as a 2-mg/kg IV bolus and then repeated every 5 minutes until the symptoms resolve to a maximal dose of 10 mg/kg. This protocol may be repeated every 10-15 hours. Once the patient has responded, oral therapy may be initiated at 4-8 mg/kg/day in four divided doses for 3 days.

References
BIBLIOGRAPHY

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  • Gross RJ, Caputo GM (eds): Kammerer and Gross’ Medical Consultation, 4th ed. Philadelphia, Lippincott Williams & Wilkins, 2003.
  • Eagle KA et al: ACC/AHA guideline update for perioperative cardiovascular evaluation for noncardiac surgery-executive summary. J Am Coll Cardiol 39:542-53, 2002.
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  • Berl T, Schrier RW: Disorders of water metabolism. In Schrier RW (ed): Renal and Electrolyte Disorders, 5th ed. Philadelphhia, Lippincott-Raven, 1997, pp 32-72.
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  • Hull RD, et al: Low-molecular-weight heparin prophylaxis using dalteparin extended out-of-hospital versus in-hospital warfarin/out-of-hospital placebo in hip arthroplasty patients. Arch Intern Med 160:2208-2215, 2000.

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